SPC 0700Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1120 PM CST Thu Dec 10 2020

Valid 121200Z - 131200Z


The risk for severe thunderstorms appears negligible across the
U.S., Saturday through Saturday night.

Much of the U.S. appears likely to remain most prominently under the
influence of a generally zonal belt of westerlies emanating from the
mid-latitude Pacific through this period.  Models indicate that this
regime will include a number of significant progressive short wave
perturbations, a couple of which appear likely to support fairly
significant surface cyclogenesis to the lee of the southern Rockies.

While cyclogenesis may commence across parts of the southern Great
Plains into middle Mississippi Valley today through tonight, it
appears that the most substantive deepening will occur across the
middle Mississippi Valley through southern portions of the Great
Lakes region on Saturday.  This will be accompanied by a significant
cold front which is forecast to surge east of the Mississippi Valley
into the Appalachians, while stalling across the lower Mississippi
Valley into the southern Great Plains, Saturday through Saturday

In association with these developments, large-scale forcing for
ascent and strengthening deep-layer wind fields probably will become
conditionally supportive of increasing convective potential,
possibly across a sizable portion of the Ohio Valley, and perhaps
the central and eastern Gulf Coast states.  However, based on latest
observational data and forecast soundings, a combination of
weak/limited Gulf moisture return to the warm sector and relatively
warm and/or warming layers aloft will considerably inhibit the risk
for thunderstorm development.

Thermodynamic profiles most conducive to convection capable of
producing lightning may be confined to areas beneath mid-level
cooling, to the north of a strong cyclonic mid-level jet streak
nosing into the lower Ohio Valley by 12Z Saturday.  Models suggest
that this activity may be largely focused within weak elevated
destabilization to the northeast of the surface cyclone, above the
warm frontal zone, as the mid-level speed maximum rapidly propagates
into and through the upper Ohio Valley during the day.

Forecast soundings (particularly the NAM) do suggest some potential
for very weak boundary-layer based destabilization within the warm
sector, beneath an evolving dry slot across parts of Illinois into
Indiana by midday Saturday.  Given the potentially strong deep-layer
mean wind fields and vertical shear, this will need to continue to
be monitored in later outlooks for this period.  However, guidance
currently suggests that mid-level subsidence and warming will tend
to inhibit boundary-layer based storm development.

..Kerr.. 12/11/2020

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